"Tuna and swordfish collected from some California grocery stores and sushi restaurants contained mercury levels as much as three times the threshold that authorizes federal food regulators to pull seafood from shelves, according to a study by an environmental health group.

And despite pervasive concerns about the toxic heavy metal in fish, not one of the restaurants and fewer than half of the grocery stores displayed signs warning consumers about the risks of mercury exposure, according to GotMercury.org, a public health advocacy group in San Francisco."